Ships which comprise propulsion assemblies having water jet drive systems can suffer from the problem of air ingestion into the water jet, or, in the case of propellers, when the propeller lifts out of the water. This is referred to as “broaching”. Such ingestion or broaching can cause a sudden drop in load on the engine and on the drive system, which can lead to problems. One way of attempting to overcome this problem is by the use of an engine fuel cut-off when the effects of such air ingestion or broaching are detected. This mechanical cycling can lead to a reduction in the life of the components and the need to design stronger and, hence, heavier and more expensive components.
In the case of fast ships, air ingestion can occur for a substantial part of this operation and, thus, any detrimental effect will be significantly increased.